1. Field of the Invention
The present invention refers to a tubular molded object made of a fiber reinforced thermoplastic resin plastic (FRTP), and relates to a material for FRTP molded objects to be used for producing FRTP tubular molded object as well as to the FRTP tubular molded object produced using the material for FRTP molded objects.
2. Description of Related Art
Materials for FRTP molded objects, which can be used for producing FRTP tubular molded objects such as racket frames, are conventionally known, such as
a cylindrical sleeve, which is formed by preparing a matrix fiber by spinning a thermoplastic resin for a matrix, such as polyamide and polycarbonate, into a fiber; mixspinning a matrix fiber tow consisting of the matrix fiber and a reinforcing fiber tow consisting of glass fiber, carbon fiber, or the like, into a yarn having a round cross section; and braiding this yarn into a sleeve;
a completely-impregnated tape which is obtained by impregnating a reinforcing fiber with a melted thermoplastic resin;
a partially-impregnated tape which is obtained by impregnating a reinforcing fiber with a thermoplastic resin only at the periphery thereof; and
a uni-directional cloth which is obtained by mix-weaving a reinforcing fiber and a resin fiber.
However, in the case when an FRTP tubular molded object is produced using the conventional sleeve, since a carbon fiber tow having a large tex number (for example, a carbon fiber tow of 12 K), which is inexpensive, is used as the reinforcing fiber tow in the yarn, the reinforcing fiber tow is thick, having a large diameter. Therefore, large spaces are formed around the intersections of the reinforcing fibers, which may remain as voids or resin rich parts in the FRTP tubular molded object. Thus, the FRTP tubular molded object has a reduced strength. Furthermore, since the intersection of the reinforcing fibers becomes thick, it is difficult to uniformly impregnate the reinforcing fibers with a resin. Therefore, the thus-obtained FRTP tubular molded object has a disadvantage in appearance, since it is susceptible to wrinkling and resin-richness.
In the case when the conventional yarn is used, since the yarn is thick, having a large diameter, a sleeve obtained therefrom becomes thick, and the weight per unit length becomes large. Therefore, when an FRTP tubular molded object which is desired to have a light weight and a high strength, such as a racket frame, only about three layers of the sleeves can be layered; thus, freedom of design is limited and strength is not satisfactory.
Furthermore, when a sleeve is made by braiding a conventional yarn, the reinforcing fiber becomes fuzzy and frayed. In such a case, there are problems in that dust is produced from the reinforcing fiber and in that the strength of the obtained FRTP tubular molded object is reduced.
The above completely-impregnated tape is not flexible, since it is an FRTP itself. Therefore, it is difficult to make a sleeve by braiding the completely-impregnated tape. Moreover, it is difficult to wind the completely-impregnated tape around a core material in the production of an FRTP tubular molded object according to a filament winding method or the like.
The above partially-impregnated tape may be comparatively flexible; however, it is expensive, and thus an FRTP tubular molded object obtained therefrom is also expensive. Furthermore, some partially-impregnated tapes are not flexible, and it is difficult to produce a sleeve with such a rigid tape and to wind it around a core material, in a similar manner to the above completely-impregnated tape.
The above unidirectional cloth is expensive. Using the uni-directional cloth, it is difficult to impregnate the reinforcing fiber with the resin fiber. When mix-weaving the reinforcing fiber and the resin fiber, the reinforcing fiber becomes fuzzy.